1. Field of the Invention
The invention relates to a process for the manufacture of reinforced polyurethane foams based on the reaction of organic polyisocyanates and polyols in the presence of filler dispersions. More specifically, this invention relates to a process of manufacturing reinforced polyurethane foams by the in situ crushing of organic and/or inorganic fillers in polyisocyanates or polyols to particle sizes of less than 7 microns.
2. Prior Art
It is a known fact to produce polyurethane foams with varied physical properties by reacting compounds with a plurality of active hydrogen atoms, particularly polyhydroxy compounds containing polymers as reinforcing agents, with polyisocyanates, chain extension agents, cross-linking agents, foaming agents, activators, emulsifiers, and other additives. If the components are suitably chosen, flexible as well as rigid foams, lacquers, coatings or elastomers can be produced in this manner.
For many areas of application, the viscosity of the polymer-polyol mixture used is an important consideration in the manufacture of polyurethane plastics. This is particularly true for the manufacture of polyurethane foams where the polymer-polyol mixture must be capable of being pumped through metering devices as well as being mixed in mixing chambers homogeneously as quickly as possible with the isocyanate component as well as with the additives such as activators, emulsifiers, water and/or foaming agents. For this reason, viscosities as low as possible are desirable in the manufacture of polyurethane foams. Poor mixing of the reactants during the polyurethane manufacture due to high viscosities result in inhomogeneties and the polyurethane composition produced is of inferior quality insofar as the physical properties are concerned.
It is furthermore known that the addition of polymerizates containing groups which react with isocyanates can increase the load-bearing capacity of low density flexible polyurethane foams (U.S. Pat. No. 3,523,093). An initial drawback of the referenced process is that the polymers suitable as fillers must be polymerized in the presence of organic solvents namely alcohols and mercaptans containing monofunctional active hydrogen atoms. If one proceeds according to the data of this publication and uses the brittle polymerizate powders described therein as fillers, the viscosity of the mixture containing higher concentrations of the polymerizate in the polyhydroxy compound increases to such a degree that the mixture is difficult to handle since it no longer is free flowing. Also, since the polymerizate powders precipitate relatively quickly, the dispersions are not storage-stable.
This U.S. patent further indicates that the polymerizates described therein cannot be used when a certain molecular weight has been exceeded since the viscosity of the polymer-polyol mixture will then become so great that it can no longer be used for the manufacture of polyurethanes. Highly viscous polymer-polyol mixtures cannot be used without special measures for processing, for instance, on high pressure foaming machinery.
According to U.S. Pat. No. 3,869,413, flexible polyurethane foams are produced from polyisocyanates and a polyether polyol which contains a polymer in latex form having a particle size of 1000 to 10,000 angstrom in a concentration of 2 to 50 percent by weight based on the polymer polyol mixture, the said polymer being obtained by the polymerization of one or more ethylenically unsaturated monomers which are free of groups which could react with isocyanate or hydroxyl groups under urethane formation conditions. A disadvantage of this process is that the mechanical properties, in particular the tensile strength of the flexible foams produced in this manner, is unsatisfactory. Furthermore, the solid contents of the aqueous polymer dispersion, particularly in the case of styrene-acrylonitrile copolymerizates containing large amounts of acrylonitrile, are extremely low so that high processing costs are connected with the removal of water.
Also known are dispersions of copolymers, preferably styrene-acrylonitrile copolymers, in hydroxyl group containing polyethers (German Pat. Nos. 12 22 669, 11 52 536, and 11 52 537). If the vinyl monomers are copolymerized directly in the polyols, the resulting particles are generally so small that there is no tendency towards sedimentation. The disadvantage of these dispersions is, however, that they must be free of monomers in order to result in foams which are as odorless as possible and which are toxicologically unobjectionable. This means that the monomers must be separated from the dispersion, for instance, with the aid of thin film evaporators.
The state-of-the-art also includes processes where inert fillers of organic or inorganic nature are incorporated into one of the starting components for the foaming or which are directly incorporated into the foaming mixtures, for instance, in the mixing chamber of a foaming machine. However, these processes also have serious drawbacks. Using traditional fillers, it is thus extremely difficult to produce dispersions having such a fine particle distribution that storage stable mixtures are obtained. The danger of sediment formation is always very pronounced requiring those dispersions to be stirred more or less intensively in order to avoid difficult redispersing processes. Among these are polyurethane foams filled with barium sulfate.